Question about QAudioOutput playing blank sound

QtMultimedia's QAudioOutput ...
play a blank *.wav file(all dates are zeros with signedint and 16bit), the sound will start with 'poo'
why this happen?
and how can I avoid this problem?
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QAudioFormat format;
format.setSampleType(QAudioFormat::SignedInt);
//using this or QAudioFormat::UnSignedInt is same effect.
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